1. Field of the Invention
The present invention relates to a lens-fitted photo film unit having an aperture stop device. More particularly, the present invention relates to a lens-fitted photo film unit having an aperture stop device, in which an aperture stop can be changed over easily and exactly, and which has a simplified structure.
2. Description Related to the Prior Art
There is a lens-fitted photo film unit pre-loaded with unexposed photo film as a single-use camera. A type of the lens-fitted photo film unit accommodates a flash device, which enables an exposure even in a room or a place with weak ambient light, for example at night. The lens-fitted photo film unit has a simple shutter mechanism, simple photo film winding mechanism and the like which can remarkably lower the cost of the lens-fitted photo film unit. The lens-fitted photo film unit is widely used because of easy handling and availability.
The widely used type of the lens-fitted photo film unit has a fixed aperture stop and a fixed shutter speed. There is no control of an exposure in consideration of object brightness. However, the accommodated negative photo film has sufficient latitude, which can result in producing photographic prints with acceptably high image quality in view of ordinarily photographed scene without extreme patterns of object light.
Furthermore, there is a known type of the lens-fitted photo film unit with a mechanism for changing over the aperture stop stepwise according to turning on and off of emission of flash light. Specifically, the aperture stop is changed over to a larger aperture stop state if the flash emission is turned on. Note that an f-number of the optical system is smaller when the larger aperture stop is set. So a background object behind a principal object is photographed at an adequate exposure amount in spite of lack of reach of the flash light to the background object. The principal object is reliably illuminated by the flash light, and as a result, can be reproduced at a suitable density together with the background object.
However, there are numerous conditions in scenes and objects that users wish to photograph. The two-step changeable type of the aperture stop and the sufficient latitude of the photo film cannot be utilized for agreeably taking a photographic object under a certain condition. For example, an underexposure may occur in photographing a scene, which cannot be recorded by any means acceptably in known types of the lens-fitted photo film unit. It may be conceivable to raise the number of the steps at which the aperture stop is changeable. However, there occurs a problem of higher difficulty in the manual operation of a user, because he or she is obliged to determine a suitable one of the plural steps of the aperture stop. Also, it may be conceivable to automate the changes of the aperture stop according to changes in object brightness. However, a selector mechanism for this purpose must be incorporated, and raise the manufacturing cost of the product. This is inconsistent to the easy availability of the lens-fitted photo film unit.
In view of the foregoing problems, an object of the present invention is to provide a lens-fitted photo film unit having an aperture stop device, in which an aperture stop can be changed over easily and exactly, and which has a simplified structure.
In order to achieve the above and other objects and advantages of this invention, a lens-fitted photo film unit pre-loaded with photo film is provided, in which a photometric circuit measures object brightness of a photographic object, and determines which of high brightness and low brightness the object brightness is according to comparison with a predetermined reference brightness level. A mode selector determines a selected one of an AE mode and a night scene mode. An aperture stop device changes over a photographic light path in a selected one of a small aperture stop state, a middle aperture stop state, and a large aperture stop state, the middle aperture stop state having a greater aperture diameter than the small aperture stop state, the large aperture stop state having a greater aperture diameter than the middle aperture stop state, wherein the aperture stop device sets the light path in the small aperture stop state when the AE mode is determined and also when the object brightness is the high brightness, sets the light path in the middle aperture stop state when the AE mode is determined and also when the object brightness is the low brightness, and sets the light path in the large aperture stop state when the night scene mode is determined.
Furthermore, a flash device is driven when the night mode is determined, for applying flash light to the object.
Furthermore, a shutter mechanism is settable at a selected one of high and low shutter speeds, for providing the photo film with an exposure by opening and shutting the light path. A shutter speed changer sets the shutter mechanism at the high shutter speed when the AE mode is determined, and sets the shutter mechanism at the low shutter speed when the night scene mode is determined.
The aperture stop device includes a stationary aperture stop plate, disposed in a stationary manner, having a large aperture stop opening in the light path, for defining the large aperture stop state. At least one movable aperture stop plate has a middle aperture stop opening and a small aperture stop opening, the middle aperture stop opening being smaller than the large aperture stop opening, the small aperture stop opening being smaller than the middle aperture stop opening, wherein the movable aperture stop plate defines the large aperture stop state when set away from the light path, and the middle and small aperture stop openings define respectively the middle and small aperture stop states when set in the light path.
The aperture stop device sets the light path in the small aperture stop state when the night scene mode is determined and also when the object brightness is the high brightness, and sets the light path in the large aperture stop state when the night scene mode is determined and also when the object brightness is the low brightness.
Furthermore, a flash switch is externally operable, for turning on the flash device when rendered conductive, and for turning off the flash device when rendered non-conductive. A lock mechanism is actuated when the night scene mode is determined, for keeping the flash switch conductive by locking, so as to inhibit the flash switch from being non-conductive.
Furthermore, a flash adjusting unit changes over flash light of the flash device at a selected one of at least a high light amount and a low light amount, the high light amount being obtained by full flash emission of the flash device, the low light amount being obtained by restricting flash emission of the flash device according to reflected flash light from the object.
In a preferred embodiment, the aperture stop device includes a stationary aperture stop plate, disposed in a stationary manner, having a large aperture stop opening in the light path, for defining the large aperture stop state. A middle aperture stop plate has a middle aperture stop opening with a smaller aperture diameter than the large aperture stop opening, movable between first and second positions, wherein the middle aperture stop plate, when in the first position, sets the middle aperture stop opening in the light path to define the middle aperture stop state, and when in the second position, is away from the light path. A small aperture stop plate has a small aperture stop opening with a smaller aperture diameter than the middle aperture stop opening, movable between third and fourth positions, wherein the small aperture stop plate, when in the third position, sets the small aperture stop opening in the light path to define the small aperture stop state, and when in the fourth position, is away from the light Path.
The AE mode and the night scene mode are determined by shifting the mode selector in respectively the AE position and the night scene position. The aperture stop device further includes a middle aperture stop transmission mechanism for shifting the middle aperture stop plate to the first position when the mode selector is in the AE position, and for shifting the middle aperture stop plate to the second position when the mode selector is in the night scene position. A small aperture stop setting mechanism shifts the small aperture stop plate to the third position when the object brightness is the high brightness, and shifts the small aperture stop plate to the fourth position when the object brightness is the low brightness.
The small aperture stop setting mechanism includes an actuator.
Furthermore, a flash button portion is movable between on and off positions, for rendering the flash switch conductive when in the on position, and for rendering the flash switch non-conductive when in the off position. The mode selector includes a mode button portion movable on an orbit extending along a moving orbit of the flash button portion, and movable between an AE position representing the AE mode and a night scene position representing the night scene mode. The lock mechanism is a lock projection, disposed to project from the mode button portion, for retaining an end part of the flash button portion near to the off position when the mode button portion is set in the night scene position, to set the flash button portion forcibly in the on position, the flash button portion being inhibited from coming back to the off position.
The flash adjusting unit determines the high light amount when the small aperture stop state is set, determines a middle light amount when the middle aperture stop state is set, and determines the low light amount when the large aperture stop state is set, so as to prevent overexposure in the middle and large aperture stop states.
The flash adjusting unit includes a flash adjustment photo sensor for detecting the reflected flash light from the object. A light amount integration circuit obtains an integrated light amount by integration of a signal of the reflected flash light. A quench circuit is enabled in response to a signal of the low brightness from the photometric circuit, for quenching the flash emission of the flash device when the integrated light amount comes up to a reference value of the middle or low light amount, the quench circuit being disabled in response to a signal of the high brightness from the photometric circuit, to determine the high light amount.
The flash adjusting unit further includes a light amount selector, shifted by changing over of the mode selector, for selecting the low light amount when the night scene mode is determined, and for selecting the middle light amount when the AE mode is determined.
The light amount selector includes a light reducing filter, offset from the light adjustment photo sensor when the night scene-mode is determined, and set in front of the light adjustment photo sensor when the AE mode is determined, for weakening the reflected flash light being detected, to slow a rise in the integrated light amount, the flash emission of the flash device being continued until the flash light increases up to the middle light amount higher than the low light amount.
The mode selector has a movable plate, and the light reducing filter is secured fixedly on the movable plate.
The shutter mechanism includes a shutter opening for defining the light path. A shutter blade is movable pivotally in a shut position and first and second open positions, for shutting the shutter opening when in the shut position, and for opening the shutter opening when in the first and second open positions, the second open position being disposed between the shut position and the first open position. A shutter blade driving unit moves the shutter blade pivotally from the shut position toward the first open position, and then back to the shut position. The shutter speed changer includes a movable stopper, movable between an offset position and a blocking position, set away from the moving path of the shutter blade when in the offset position, for enabling the shutter blade to reach the first open position, to determine the low shutter sped, the movable stopper extending into the moving path of the shutter blade when in the blocking position, for disabling the shutter blade from moving beyond the second open position toward the first open position, to determine the high shutter speed by shortening time for backward movement. A transmission mechanism sets the movable stopper in the offset position when the night scene mode is determined in the mode selector, and sets the movable stopper in the blocking position when the AE mode is determined.